In the manufacture of electrical motors, particularly three-phase alternating current electric motors, stator coils are wound in and through a laminated iron core to produce a round stator core. Conventionally, such wound stator cores are made of copper and coated with a varnish material (such as an insulating resin coating) which insulates the copper wires of the stator coils from each other, the copper wires from the iron of the stator core, and the copper wires from the motor housing. In addition, the insulating resin coating or enamel mechanically stabilizes the wires in the stator core so that the vibration of the motor during use does not cause the wires to vibrate and undesirably wear through their enamel insulation thereby exposing the copper stator coils.
Moreover, in the high field intensity environment of an electrical motor, an insulating resin coating is subject to breakdown from oxide erosion resulting from surface corona and embedded corona. Particularly, high field intensity leads to the generation of oxygen plasma which, in turn, oxidizes and breaks down an insulating resin. It is desirable to provide an insulating resin with corona resistance that can lead to the manufacture of electrical motors having a longer life.
Accordingly, curable electrical component coatings include inorganic additives to achieve the desired surface electrical stress endurance. Such inorganic additive materials include alumina, silica and fumed metal oxide particulate additives and other non-transparent materials. Many inorganic additives are by nature resistive to high temperature processing, both in production and in use, and they are resistive to oxidative degradation. Most inorganic additives, however, due to their compositional and physical makeup, require the use of high shear mixing when incorporated into a polymer to achieve a uniform, homogeneous composition. High shear mixing inherently creates voids in the resulting polymer coating due to the entrapment of air in the protective polymer coating mixture. The presence of voids in the cured polymer coating allows corona generation which attacks the underlying substrate and degrades the polymer coating itself under electrical stress when in use. Accordingly, it is desired to provide an additive which does not require high shear mixing and/or which does not lead to the presence of voids in a polymer which it is incorporated.
In photocurable resin systems, using non-transparent material additives with photocure processing techniques results in non-uniform curing, as the light energy curing agent may unevenly penetrate the curable resin, due to particle blockage and scattering, thus curing some resin segments and not curing others. Another problem caused by the same uneven, non-uniform penetration of the various additives is the premature cure of the resin. When using a photo initiated curing process, it is generally necessary to have particles of less than 0.2 microns. Particles in excess of 0.2 microns are capable of scattering light, thus potentially resulting in uneven curing. Commercially available particulate fillers which require high speed mixing to maintain homogeneity tend to agglomerate causing regions of higher particle concentration and regions of lower concentration. This can lead to accelerated oxidation in the particle-poor regions. Accordingly, it is desired to provide an additive which does not agglomerate, which is small in size, transparent in nature and/or capable of uniform distribution.
One problem with using metal oxide particulate material in a liquid substance is the propensity for precipitation of the material from a solution over time, thus limiting the shelf life of the solution. For example, the use of commercially available fumed alumina or silica results in precipitation of the particulate metal oxide material after about one week in storage. Since fumed alumina or silica is of high viscosity, increased amounts of solvent are needed to attain a coatable composition. Accordingly, it is desired to provide an additive which does not precipitate from solution and/or has a desirable viscosity.
U.S. Pat. No. 4,760,296 generally relates to the inclusion of organosilicates or organoaluminates as the organo-metallic material of choice to achieve improved electrical stress endurance of an epoxy resin system. The '296 patent also relates to organoaluminates such as aluminum acetylacetonate and aluminum di-sec-butoxide acetoacetic ester chelate, which can be used to produce clear resins. However, the organoaluminum compounds of the '296 patent are not suitable for a variety of resin systems. This is because they tend to (1) plasticize the cured articles, (2) generate nonuniform distribution of the additives in the cured articles, and/or (3) bleach out with aging. The same three disadvantages are associated with using fumed aluminum oxide in resin systems. Using fumed aluminum oxide also involves the disadvantages that a clear solution cannot be formed and that the viscosity is undesirably high, further contributing to the creation of voids in the resulting coating thus rendering the coating susceptible to corona attack.
Plasmas are useful for etching metals, semiconductors and dielectrics during the processing of microelectronic materials such as wafers. Plasmas are also useful for cleaning, de-scumming, stripping and passivating various surfaces of microelectronic materials. Plasma is an unstable mixture of positive ions, negative ions and free radicals. Examples of plasma include energized silicon tetrafluoride, Freons and oxygen. Accordingly, a plasma environment is a very severe and potentially damaging environment, especially to polymeric materials. In the specific case of oxygen, monoatomic oxygen attack (oxygen plasma) can be very damaging to polymeric materials. This can be a problem if it is desired not to damage a polymeric substance in a plasma environment. It is therefore desirable to provide a polymeric substance which is plasma resistant.
These problems are minimized and/or eliminated by using the oxygen plasma resistant polymers made with metal oxide sols of the present invention.